Discharge-gap device



.Patented Nov. 15,1927. i l

Y 1,649,035 PATENroFFlcl-z.

,uns L. needy, or' PITTSBURGH, PENNsYLvANIA, AssIGNon To wnsTINGnoUsn 'nnncTnIc a MANUFACTURING COMPANY, AbonPonATIoN or PENNSYLVANIA DISCHARGE-GAP DEVICE.

Application nled December 29, 1925. Serial No. 78,113.

My invention relates to discharge gap devices, and it has particular relation to such devices `utilized to protect electric circuits andapparatus against surge voltages. One object of my invention is to provide a discharge gap device comprising fourl gap' electrodes so arranged with respect to each other as to constitute six discharge gaps of equal gap distance.

Another object of my invention is to pro'- vide an evacuated discharge gap device comprising tour electrodes so mounted as to constitute the corners cfa regular tetrahedron, all the gaps between said electrodes having substantially the same break-down voltage.

In connection with the development of the supervisory control systems for modern power distribution circuits, the need has been felt for lightning arresters that would pron vide, in a compact Jform, a plurality of.

equally spaced discharge gaps, since such supervisory circuits usually comprise a large number of wires to be Iprotected, and it is inconvenient, aswell as' expensive, to provide .25 such protection by lmultiplying the number of individual protective units.' p

-According' to my invention, I greatly simplify the wiring, as well as` the maintenance work in connection with the protective equipment of supervisory control circuits, or similar multi-wire systems, by providing a protective gap discharge device having four electrodeswhich are so spaced as to provide six equidistant gaps having the same breakdown voltage.

My invention will be bestunderstood by reference to the accompanying drawing, 'wherein Fig. -1 is an elevational view of a lightning 4'0 .arrester embodying my invention;

Fig. 2 is a view in detail illustrating the arrangement of theelectrodes in tle lightarrester of Fig. 1, and ig. 3 is a wirin diagram', showing a protective circuit vem odying'the lightning `ar: rester shown in Fig. 1. Referring toFig. 1, a`partially evacuated .container 1 ofiglass, for instance, has mounted therein fou' spherical electrodes 2, 3,.r 4 0 and 5 which are -so arranged that the centers l thereof constitute corners ofla regular tetrahedron, as shown in Fig. are preferably made oV l material, 'suchas-graphte--in vorder to pre- 5 vent-theoocluslonof 1 during 2. The electrodes porous conducting hachage and are held on the ends of four leading-in .conductors 6, 7, 8 andv 9 which are welded I 1to the conducting terminals of the base. The 'other pair of leading-in wires 6 and 7 which 65 are held in the press 11 disposed in the other extension 13 ofthe envelope, are so disposed that the planes ofthe two pairs of leadingin 4wires are perpendicular to each other, this arrangement facilitating the assembly and the correct lspacing of the four electrodes.

The spacing between the four spherical electrodes is approximately EL! of an inch between each pair. lnl manufacturing my arrester tube, the electrode leads are first mounted in pairs in their respective presses 11 .and 12 and then the presses are weldedl into the envelope. The tubes are e acuatedv, and lled with a suitable gas, such as argof'o at a pressure which may be of the order of from 2 to 8, inches of mercury. The gas, pressure 'is somewhat higher than that corresponding to the minimum break-down voltage of' the gaps,thereby insuring that the 35 gaps will break down between the closest points on the spherical electrodes.

If argon is used, having a minimum breakdown voltage of about 250, a voltage of 30.0 may be impressed uponv a pair of electrodes which the argon is. being slowly admitted to the evacuated tube, and the argon'admis'sion may be stopped when a visible discharge occurs. Havlng once determined the gas peressure all of the tubes manufactured'may 95 quickly and automatically filled with argon at that pressure, provided that the electrede materlal and spacing is the 4same forl all of 'the tubes.

As may be seen from Fig.,2`, the surfaces *of the four spherical electrodes constitute-@- six e'quidistant gaps. By connecting three of the electrodes to three line wires 16 of a supervisory control system or other limitedcurrent system which `is to be protected, and by connecting the fourth electrode to ground, as' shown'in Fig. 3, each of the' gaps will breakdown at the samevoltage,l securing equal protection of each element of the clrculta. V11u My multigap tube is particularly suitable for supervisory control systems and other circuits utilizing voltages not greatly in excess of normal arcing voltages of 30 or 40,-

and having sullicient series resistance to limit the current to one ampere or less. It is a property of multiga arrester tubes that the entire space within t e tube becomes ionized, so that when one gap breaks down, there is a tendency for all of the gaps to break down. When a very severe overvoltage is applied to one of the electrodes of the arrester, as would be the case if a 11,000-vo1t power line came into contact with a wire of the supervisory control system, L the arrester would break down with a glow discharge at 300 volts, and would remainjn the condition of a glow discharge as long as the current remained under about one ampere, which would'be during a very small part of a cycle. The discharge would almost immediately be converted into an are having a discharge voltage of about 40.

It is clear that, if a multigap arrester tube were applied to a llO-volt vpower line, the line voltage would produce arcs between each line electrode and the grounded electrode. In the supervisory control system to which my invention, is applied, however, the normal line voltage is incapable of maintaining an arc of one ampere or more, and hence the supply voltage for the supervisory controll is not short-circuited by the operation of the excess voltaffe arrester.

The uniibrm discharge voltage between each of the pairs of electrodes is desirable because all sorts of conditions including high voltage between any one or more of the lines and' each other or ground may be obtained"l in case of trouble on a supervisory control system, and it is desirable for the discharge to take place between the electrodes having the maximum potential difference between them, in order to quickly 'blow the high voltage fuses (not shown) with which the system is provided.

I claim as my invention: l

A1. An overvoltage discharge gap device comprising four gap electrodes having subchar e members throught e walls`of said enve ope, and a gas of reduced pressure in said envelope.

3. An over-voltage discharge device comprising a hermetically closed glass envelope having two presses on opposite sides thereof, two pairs of rigid leading-in conductors welded in said two presses respectively and extending toward each other from' opposite sides within said vessel substantially spherical discharge electrodes mounted at the inner ends 5of said conductors so that the centers of the spheres constitute the four corners of a regular tetrahedron, and a 'gas ofv reduced pressurev in said envelope.

4.. An over-voltage discharge device comprising a 'hermetically closed glass envelope aving two presses on opposite sides thereof,

said presses extending in longitudinal planes substantially at right angles to each other, two pairs of rigid leading-n conductors welded in said two presses res ectively and extending toward each other iom opposite sides within said vessel substantially spherical discharge electrodes mounted at the inner ends of said conductors so that the centers of the spheres constitute the four corners ofa regular tetrahedron, and a gas in said envelo e having suiiicient pressure to insure that t e discharge will take place between the points having the closest spacings.

In testimony whereof, I have hereunto subscribed my name this 19th day of December, 1925.

JAMES L. MCCOY. 

